SYNCHROTRON LIGHT REVEALS CHEMICAL GHOSTS OF PAST LIFE

Multidisciplinary approaches to the analyses of fossilised soft tissue have shown that endogenous organic compounds can survive through geologic time. The work presented here will show how coupling synchrotron-based X-ray and infra-red methods can serve to non-destructively resolve the survival of organic compounds derived from fossil and extant organisms, but also how spectroscopic details can assist in understanding the chemistry of exceptional preservation. Here we use Fourier Transform Infrared Spectroscopy (FTIR) to spatially resolve organic functional groups within Eocene (~50 mya) to Jurassic (~155 mya) aged fossils that show biological control on the distribution of amide and sulfur compounds. These compounds are most likely derived from the original biomaterials present in the structures analysed because other non-fossil derived organic matter from the same geological formations do not show intense amide or thiol absorption bands. Infrared maps and spectra from the fossils are directly comparable to extant samples. X-ray Absorption Spectroscopy (XAS) of sulfur in some fossil tissues shows it is present in several oxidation states, including organic sulfur compounds and inorganic sulfate minerals. By using this information to tune the incident X-ray beam energy to a value below the critical excitation energy for inorganic sulfur, we were able to use Synchrotron Rapid Scanning X-ray Fluorescence (SRS-XRF) to discreetly map organic sulfur in discrete biological structures. This approach resolves fossil-derived organic compounds with striking detail. In addition, in this and other fossil specimens, XAS analysis of trace metals correlated with soft tissue structures indicating that a significant and in some cases dominant portion of trace metal inventory is organically coordinated within tissue residues. Quantitative synchrotron-based XRF point analyses are presented to show that concentrations determined within fossils are comparable to those of extant organisms, that phylogenetically bracket fossil samples. A taphonomic model involving ternary complexation between fossil bio-derived organic molecules, divalent trace metals, and silicate surfaces are here presented to explain the survival of the observed compounds.